Internal combustion engine arrangement with EGR drain system

ABSTRACT

An internal combustion engine arrangement includes an EGR circuit connecting a exhaust circuit to an intake circuit to incorporate a portion of exhaust gases in the intake gases, at least one turbine located, and a dedicated drain conduit which connects the EGR circuit to the exhaust circuit. The EGR circuit includes at least one low position point and the dedicated drain conduit permanently connects the low position point of the EGR circuit to the exhaust circuit upstream of the turbine.

BACKGROUND AND SUMMARY

The invention relates to an internal combustion engine arrangementhaving an exhaust gas recirculation (EGR) circuit.

As it is well know, an internal combustion engine may comprise a seriesof cylinders, an intake circuit for circulating intake gases to thecylinders and an exhaust circuit for collecting and evacuating exhaustgases from said cylinders. Many modern engines are now equipped with aturbo-charging system to enhance their efficiency, thereby having atleast one turbine located in the exhaust circuit for recovering energyfrom the exhaust gases. For reasons mainly related to a better controlof noxious emissions by the engine, it is well known to equip the enginewith an EGR circuit connecting the exhaust circuit to the intake circuitto incorporate a portion of exhaust gases in the intake gases.

The portion of the exhaust gases which circulate in the EGR circuit,which will be referred to hereinafter as EGR gases, are those gaseswhich result from the combustion of the air/fuel mixture in thecylinders. EGR gases comprise mainly carbon dioxide and water, but mayalso comprise nitrogen oxides, un-burnt hydrocarbons, carbon monoxideand other residues such as particles and soot. Among all thesecomponents, water is certainly the least harmful component in terms ofpollution, but it nevertheless raises some difficulties. Indeed, it hasappeared that at least in some EGR circuit designs, the water containedin the EGR gases, initially under vapor form due to the temperature ofthe exhaust gases, may condense in the EGR circuit. Of course, the riskis maximum in engine arrangements where the EGR circuit comprises acooler to cool down the EGR gases before they are introduced in theintake circuit, and it is of particular relevance when the engine hasnot reached its full operating temperature, while starting and/or undercold temperatures.

The amount of water which may condense will vary according to the enginedesign, but also depending on the type of fuel burnt in the engine.Although water condensation may happen in petrol engines, in Dieselengines and in gas engines, it has proved to be particularly importantin the case of gas engines, simply because the amount of water producedby the combustion of gas is proportionally more important than withother fuels.

Water condensation in the EGR circuit may lead to undesired results.First, the water will tend to accumulate at any low position point inthe EGR circuit, that is any point of the circuit which has an altitudelower than its neighboring points on both sides. It is to be noted thata given circuit may comprise several low position points. Such lowposition points may be in a conduit portion of the circuit, in a coolerassembly or can be located at a valve level when the valve is closed.The amount of water which may condense can be quite important,especially during engine start-up.

If the accumulated water is still present when the engine is shut down,it will stay at least until next start-up, and may cause corrosionissues at the low position point. Another potential problem is that, atcertain times, a quantity of accumulated water may burst into the intakecircuit and be fed, still under liquid form, to the cylinders. If theamount of water thus fed to the cylinders is not insubstantial, it mayseverely affect the combustion process, resulting in engine jerk andincreased production of noxious compounds in the cylinder.

In order to prevent such problems, it has already been suggested toequip the EGR circuit with drain systems to prevent or at least removeaccumulated water.

Document JP-2001.193578 discloses an EGR circuit having a drain valve.The drain valve is a normally-open ball valve where the ball isspring-biased to the open position in the absence of pressure in the EGRcircuit, so as to permit condensed water to escape. As soon as the EGRcircuit is under pressure, the ball valve is automatically closed. Sucha pressure controlled valve does not allow accumulated water to bedrained when the EGR circuit is in use. The drain valve is arranged at alow position point in the EGR circuit, very close the exhaust circuit,and when the valve is opened, it discharges directly in the atmosphere,which is of course not optimum due to the fact that noxious substancesmay be discharged to the atmosphere, amounting to pollution

Documents JP-7.269417 and JP-8.46964 both disclose an EGR circuit with acondensed-water collector which can be drained through a dedicatedcontrolled purge valve. The valve discharges directly to the atmosphere,with the above mentioned pollution problem, and this dedicatedcontrolled valve represents an increased cost.

Document JP-2005.256.679 shows an engine having an engine arrangementwhere a dedicated controlled drain valve is provided at a low positionpoint in the intake circuit between the EGR mixer and the intakemanifold.

Document JP-2006-274961 shows an EGR circuit with a dedicated drainconduit which connects the EGR circuit to the exhaust circuit and whichis equipped with a cyclone-type gas/water separator having a dedicatedcontrolled drain valve. The separator is of course a cumbersomeapparatus, also representing an additional cost in addition to the costof the dedicated controlled valve.

Document US-2007/0084206 also shows an EGR circuit with a dedicateddrain conduit which connects the EGR circuit to the exhaust circuit andwhich has a dedicated controlled drain valve, with one embodiment havingthe drain valve combined with the conventional EGR valve as a three wayvalve. As in the previous document, the drain valve is connected to theexhaust circuit downstream of the turbine of a turbo-compressor. In thelatter document, the drain valve appears to be only opened when the EGRvalve is closed, so that no draining appears to be possible when the EGRis required.

In view of the above, it appears the there is still the need for a cheapsolution to the problem of water accumulation which nevertheless doesnot cause unnecessary pollution of the ambient air and may neverthelessoperate in a wide range of engine operating conditions.

An aspect of the invention provides for an internal combustion enginecomprising:

-   -   an EGR circuit (32) connecting a exhaust circuit (20) to an        intake circuit (16) to incorporate a portion of exhaust gases in        the intake gases,    -   at least one turbine (26) located; and    -   a dedicated drain conduit (46) which connects the EGR circuit        (32) to the exhaust circuit (20);        characterized in that the EGR circuit comprises at least one low        position point and in that the dedicated drain conduit        permanently connects said low position point of the EGR circuit        to the exhaust circuit upstream of said turbine.

According to other features of an engine arrangement:

-   -   the engine may comprise one or several cylinders;    -   the intake circuit is designed for circulating intake gases to        the cylinder(s);    -   the exhaust circuit is designed for collecting and evacuating        exhaust gases from said cylinder(s):    -   the turbine located in the exhaust circuit is designed for        recovering energy from the exhaust gases.

DESCRIPTION OF FIGURES

FIG. 1 is a schematic diagram of an engine arrangement according to theinvention.

FIGS. 2 and 3 are schematic graphs showing the comparative pressurelevels in the intake and exhaust manifolds of an internal combustionengine, for two sets of engine operating conditions.

DETAILED DESCRIPTION

FIG. 1 very schematically shows an internal combustion enginearrangement 10 having an engine block 12 comprising as series ofcylinders 14, which could be of any number, the invention being alsoapplicable in the case of a mono-cylinder engine. An intake circuit 16,comprising an intake conduit 18 and an intake manifold 19, provides theengine cylinders with intake gases. An exhaust circuit 20, comprising anexhaust manifold 22 and an exhaust conduit 24 collects the exhaust gaseswhich result from the combustion of the intake gases in the cylinders14. According to the invention, the engine further comprises at leastone turbine 26 located in the exhaust circuit 20 to recover a part ofthe energy contained in the exhaust gases.

According to a preferred embodiment of the invention, the arrangement 10comprises also a compressor 28 in the intake circuit to compress theintake gases which are fed to the cylinders 14.

In the described embodiment of the invention, the engine is aturbocharged engine wherein the turbine 26 in the exhaust circuit drivesthe compressor 28 in the intake circuit. Nevertheless, the inventioncould also be applied in an arrangement where the turbine drives anotherapparatus, such as an electric generator or a gear train of aturbo-compound system. Similarly, the preferred embodiment of theinvention could comprise a compressor 28 driven not by the turbine 26but driven mechanically by the engine crankshaft. The engine could alsocomprise other compressors and/or other turbines located upstream ordownstream of the above mentioned compressor 28 and turbine 26.

Depending on the engine arrangement, such as on the type of fuel burntby the engine, and on whether fuel injection is of the direct type orindirect type, the intake circuit may comprise various additionalcomponents. For example, in the represented embodiment, the intakecircuit comprises a charge air cooler 30 for cooling the intake gas. Thecharge air cooler 30 is located in the intake conduit between thecompressor 28 and the intake manifold. Similarly, depending on theengine arrangement, the exhaust circuit 20 may comprise additionalcomponents, not shown on the figure, especially components dedicated tothe treatment of the exhaust gases to reduce their noxiousness and toreduce the noise they may generate. The exhaust manifold could bedivided in sub-manifolds, each dedicated to only one group of cylinders.

The engine arrangement according to the invention also comprises an EGRcircuit 32. The EGR circuit shown on FIG. 1 comprises an EGR conduit 34which is fluidly connected by an upstream extremity 36 to the exhaustcircuit 20 and, by a downstream extremity 38, to the intake circuit 16in order to provide a part of the exhaust gases, hereinafter called EGRgases, to the intake circuit to be incorporated in the intake gases fedto the cylinders. The downstream extremity 38 of the EGR conduit isconnected to the intake circuit 16 through an EGR mixer 40 where the EGRgases are mixed to intake air to form the intake gases. In the example,shown, the EGR mixer 40 is located downstream of the compressor 28, butit could also be located upstream of said compressor. In the shownembodiment of the invention, the Upstream extremity 36 of the EGRconduit 34 is connected to the exhaust circuit upstream of the turbine26. In this case, it is directly connected to the exhaust manifold 22.Such a design for an EGR circuit is sometimes called short route designor high pressure design. Nevertheless, the invention is also applicablein the case of a long-route/low-pressure design where the exhaust gasesare collected downstream of the turbine and reintroduced in the intakecircuit upstream of the compressor, or in the case of a hybrid design,such as where the exhaust gases are collected upstream of the turbineand reintroduced in the intake circuit upstream of the compressor.

The EGR circuit shown on the figures also comprises an EGR cooler 42, tocool down the EGR gases, and an EGR valve 44 to control the flow of EGRgases in the EGR circuit, thereby controlling the composition of theintake gases. In the shown embodiment, the valve 44 is located on theEGR conduit downstream of the EGR cooler 42, but the reverseimplementation is also possible. The EGR circuit 32 further comprises adedicated drain conduit 46 which connects the EGR circuit to the exhaustcircuit 20.

According to the invention, the EGR circuit 32 comprises at least onelow position point 48, and the dedicated drain conduit 46 permanentlyconnects said low position point 48 of the EGR circuit 32 to the exhaustcircuit 20 upstream of the turbine 26 to evacuate condensed water ormore generally any liquid material present at low position point 48.

In the described embodiment of the invention, the low position point 48is located in the EGR circuit between the EGR cooler 42 and the EGRvalve 44. When the EGR circuit is equipped with a cooler, this locationdownstream of the cooler is particularly advantageous becausecondensation is most likely to appear in the cooler or just downstreamof the cooler. The low position point could be inside the cooler itself.Also, the location of the low position point upstream of the EGR valveis very advantageous because it implies that the drain circuit remainsconnected to the EGR circuit even when the EGR valve 44 is closed. Ofcourse, this feature is even more advantageous in a configuration where,as in the shown embodiment, the EGR valve is located in a downstreamportion of the EGR circuit, near its connection to the intake circuit,and downstream of the EGR cooler, if any. Indeed, it is then possible tohave a low position point in one of the coldest part of the EGR circuit,where condensation is most likely, while keeping the advantage of thepermanent connection of the drain conduit with the EGR circuit.

It must be understood that the EGR circuit may comprise several lowposition points. In such a case, it is possible to equip several or allof them with a drain device, but it is also possible to equip only oneof them with such device if only one of them is really prone to wateraccumulation. Indeed if the EGR circuit has a low position point nearits upstream extremity 36; the risk of having any substantial wateraccumulation in such a location is fairly small, because such a locationwill be very quickly heated by the exhaust gases.

The low position point 48 where the drain conduit 46 is connected to theEGR circuit can be located at a bottom point of a specifically designedwater accumulating chamber, or it can just be a location implied by theother constructional constraints of the arrangement and by the ordinarydesign of an EGR circuit.

In the shown embodiment, the drain conduit is connected to the exhaustcircuit 20 directly on the exhaust manifold 22 which, in most cases,will be the hottest spot of the exhaust circuit. This ensures that thewater drained through conduit 46 is efficiently vaporized as soon as itenters the exhaust circuit almost at all times.

In one embodiment of the invention, the drain system may rely on gravityto evacuate accumulated water at the low position point 48 towards theexhaust circuit. Therefore, it has to be provided that the drain conduithas its connection to the EGR circuit at a higher level than itsconnection to the exhaust circuit, and that it itself has nointermediate low position point.

Nevertheless, it can also be provided that the evacuation of accumulatedwater may be assisted by the pressure of gases in the system.

On FIG. 2 is shown a diagram showing an exemplary comparison of thevariation over time of the pressure P2 in the intake manifold and of thepressure P3 in the exhaust manifold of a turbo-compressed internalcombustion engine. Such a diagram is valid for a given set of operatingconditions, corresponding to rather low engine load conditions. FIG. 3represents the same diagram but for rather high load/high speed engineconditions.

As can be seen, the pressure P2 in the intake manifold is quite constantfor such a given state of operation of the engine. To the contrary, thepressure P3 varies over time, with pressure peaks which correspond tothe opening of the exhaust valve(s) of the cylinders. Of course,pressure variations at locations more downstream in the exhaust circuitare smoothened.

In the set of operation for which the diagrams of FIGS. 2 and 3 aretrue, the pressure P3 in the exhaust manifold is sometimes lower thanthe pressure in the intake manifold, but is higher than the pressure inthe intake manifold when the exhaust manifold pressure reaches its peaklevels corresponding to the opening of the exhaust valve(s). To ensurethat the EGR circuit may operate under such conditions, i.e. to ensurethat exhaust gases are nevertheless incorporated in the intake gases, itis known to equip the EGR circuit with a check valve system assymbolically depicted under reference 52 in FIG. 1. Such a system can beof the type described in document EP-1.098.085 and is also referred toas a reed valve. Such a system is preferably located downstream of theEGR cooler when the EGR circuit is so equipped. Such a check valvesystem permits the flow of EGR from the exhaust circuit to the intakecircuit when pressure differential is favorable (peak pressures inexhaust manifold) and prevents any backflow otherwise.

In such a design, it may therefore be useful to provide that the lowposition point 48 of the EGR circuit 32 to which the drain conduit 46 isconnected is situated downstream of the check valve system 52 andupstream of the EGR valve 44. Indeed, when the EGR valve is open,pressure at the low position point will never be lower than the pressureP2 in the intake manifold. Therefore, when pressure P3 in the exhaustmanifold falls below that pressure level, the pressure differentialbetween each extremities of the drain circuit will at least assist theflow of water from the EGR circuit towards the exhaust circuit. When theEGR valve is closed, the check valve system 52 will tend to create apressure accumulation in the portion of the conduit 34 between the checkvalve system 52 and the EGR valve 44. Therefore, when pressure P3 in theexhaust manifold falls below that pressure level, the pressuredifferential between each extremities of the drain circuit will at leastassist the flow of water from the EGR circuit towards the exhaustcircuit.

In such a design, where pressure differentials are used to assist theevacuation of water through the drain conduit 46, it will be possible toprovide a drain conduit of lesser diameter, and it may also allow morefreedom of design with respect of the height level differential betweenboth extremities of the drain circuit, compared to a design relying onlyon gravity for evacuating the condensed water. The use of a smalldiameter drain conduit is advantageous in that it will minimize theamount of EGR gases which may flow through said conduit. Indeed, it isto be noted that the drain conduit is devoid of any valve and that theconnection it establishes between the low position point of the EGRcircuit and the exhaust circuit is therefore permanent in bothdirections. Therefore, in the absence of condensed water, some amount ofEGR gases may circulate through the drain conduit 46, at least when theEGR valve 44 is open. Depending on the pressure differential at bothextremities of the drain conduit, this may result either in a parallelflow of EGR gases (un-cooled even if the EGR circuit is equipped withEGR cooler 42), or in a back-flow of gases from the EGR circuit to theexhaust circuit.

A direct advantage of the drain circuit according to the invention nothaving any valve therein is of course the cost saving in comparison withprevious systems, especially with systems having a controlled valvebecause of the additional cost of the control system. Another advantageis the reliability of the system, because it has no moving part and noelectronic part. Also, the system not only permits the draining ofaccumulated water, it also strongly limits any substantial wateraccumulation because of the permanent connection of the low positionpoint with the exhaust circuit, contrary to the prior art where theconnection is established only at certain times. Moreover, the systemaccording to the invention does not interfere at any time with thefunctioning of the EGR system and does not cause any undesired anduncontrolled pollution. Therefore, the system according to the inventionwill bring many advantages, especially in engine arrangements which aremore prone to water condensation in the EGR circuit, such as gasengines.

1. An internal combustion engine arrangement comprising: an EGR circuitconnecting a exhaust circuit to an intake circuit (16) to incorporate aportion of exhaust gases in the intake gases, at least one turbinelocated; and a dedicated drain conduit which connects the EGR circuit tothe exhaust circuit; wherein the EGR circuit comprises at least one lowposition point and in that the dedicated drain conduit permanentlyconnects the low position point of the EGR circuit to the exhaustcircuit upstream of the turbine.
 2. An arrangement according to claim 1,wherein the dedicated drain conduit is connected to the exhaust circuitat a location of lower altitude than that of the low position point ofthe EGR circuit.
 3. An arrangement according to claim 2, wherein liquidmaterial may circulate by gravity from the EGR circuit to the exhaustcircuit through the drain conduit.
 4. An arrangement according to claim1, wherein the exhaust circuit comprises an exhaust manifold collectingexhaust gases from several cylinders into one exhaust conduit, and thedrain conduit is connected to the exhaust manifold.
 5. An arrangementaccording to claim 1, wherein the intake circuit comprises at least onecompressor, and in that the EGR circuit is connected to the intakecircuit downstream of the at least one compressor, in that the EGRcircuit comprises a check valve system whereby gases may circulate inthe EGR circuit only from the exhaust circuit towards the intakecircuit, and the low position point, where the drain conduit isconnected to the EGR circuit, is located downstream of the check valvesystem.
 6. An arrangement according to claim 5, wherein the EGR circuitcomprises a cooler for cooling the gases circulating in the EGR circuit,and the low position point, where the drain conduit is connected to theEGR circuit, is located in the cooler or downstream of the cooler, andthe check valve system is located downstream of the EGR cooler.
 7. Anarrangement according to claim 5, wherein the EGR circuit comprises, inthat order, an EGR cooler, the check valve system, the low positionpoint and an EGR valve.
 8. An arrangement according to claim 1, whereinthe EGR circuit comprises a cooler for cooling the gases circulating inthe EGR circuit, and the low position point, where the drain conduit isconnected to the EGR circuit, is located in the cooler or downstream ofthe cooler.
 9. An arrangement according to claim 8, wherein the EGRcircuit comprises an EGR valve, and the low position point, where thedrain conduit is connected to the EGR circuit, is located upstream ofthe EGR valve, and the EGR valve is located downstream of the EGRcooler, the low position point being in between.
 10. An arrangementaccording to claim 1, wherein the EGR circuit comprises an EGR valve,and the low position point, where the drain conduit is connected to theEGR circuit, is located upstream of the EGR valve.